Warning bell



FIG. 1 is a front elevational view of a warning bell showing my new design, with the rear being a mirror image;

FIG. 2 is a right side elevational view thereof;

FIG. 3 is a left side elevational view thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a warning bell, as shown and described. 